1. Field of the Invention
The present invention pertains to independent wheel suspension systems and, more particularly, to independent wheel suspension systems wherein a constant velocity joint, as an indispensable component of the suspension system, is combined with a wheel motion resistance suspension assembly to provide a suspension system for a vehicle wherein the differential of the vehicle is pivotable about a first pivot axis established on the vehicle frame and a second pivot axis established on the suspension system.
2. Description of the Prior Art
The present invention has particular application to both front and rear wheel independent suspension systems wherein universal joints are used to transfer power from a power delivery unit, normally including an engine, transmission and a differential housing, through half-shaft drive axles to the driving wheels. As a vehicle moves along a road surface, the wheels naturally experience an up and down movement relative to the driving surface. This movement is referred to as jounce and rebound, and the road clearance of various vehicle components vary accordingly. If the wheels are allowed to move in a plane approximately normal to the driving surface, such up and down movements have heretofore required corresponding changes in the swing length between the wheel and the differential of the power delivery unit. Such changes in swing length are normally effected by allowing an axial adjustment either of a driving member relative to the wheels or of one member of a driving member relative to another. Because of the dynamic loads associated with these up and down movements of the wheel and the geometric movements of the suspension members as a result of the various load and road conditions experienced by the wheels of a vehicle, past suspension system design efforts have been directed toward completely isolating the drive system components from the suspension system components to prevent the application of suspension loads to the power delivery unit or torque translating drive components of a vehicle. As a result of this approach the structural design criteria of prior art vehicles is to limit the torque translating components of a vehicle to carry only torque loads to propel the vehicle and to design a separate suspension system to carry the loads associated with the up and down movement of the vehicle wheels as a result of load and/or road variations.
The foregoing jounce and rebound movements of the driving wheels relative to the road surface introduce lateral or axial thrust loads relative to the differential of the power delivery unit. The magnitude of such thrust loads is related to the transmitted torque and to road protuberances, cornering speeds, weight distribution, wheel camber, and load carried by the vehicle as well as other factors. Such axial thrust loads have been diverted from the torque translating driving joints by either suspension control members connecting the wheel assembly to other points on the chassis of the vehicle or by additional structure encasing either the torque translating half-shaft or driving joints.
Independent wheel suspension systems generally contemplate the use of two general types of universal driving joints: the Cardan-type joint and the constant velocity type joint. The Cardan-type joint consists of two yokes connected by a plain or rolling type bearing on the ends of a Cardan or cruciform-shaped cross. The cross consists of a block and two pins, one pin being smaller than the other and passing through it. Even though heat-treated alloy steels are used throughout, the small pin diameters limit the capacity of the joint to carry axial thrust loads because such axial thrust loads normally impose stresses on the pins which are multiples of the stresses associated with carrying normal driving torque. Moreover, the stresses deleteriously augment each other through vector addition. The major deterrent to using a single Cardan-type joint in an independent rear suspension system, however, is the severe limitation on the allowable angle of articulation under high torque loads. This is because the velocity ratio of the speed of the driving to the driven shaft pulsates or "knuckles" with increasing amplitudes as the angular articulation between these shafts increases. The cyclic speed pulsations significantly increase as articulation between the driving and driven joint members increase. Such speed pulsations cause correspondingly higher dynamic stresses on the Cardan cross pins and corresponding vehicle vibration and noise as loads of any appreciable inertia are translated through the joint. The higher dynamic stresses wear the joint structure to degeneratively further increase the speed variations and further limit the ability of the Cardan joint to carry high torque loads. Moreover, under thrust loads, the normal manufacturing tolerance of a Hooke's joint or Cardan joint, by themselves, cause unacceptable vibrations.
To avoid the foregoing deleterious stress and load carrying consequences of Cardan-type universal joints, their use in vehicles is generally limited to applications where the normal angular articulation between the driving and driven members is substantially less than ten degrees, usually less than three degrees. Even then, as herein above set forth, other structure is provided to divert the axial thrust loads away from the Cardan-type universal joints. For example, British Patent No. 765,659 discloses the use of a Cardan-type universal joint to carry just the driving torque. A spherical socket and a mating ball-shaped member are provided about the Cardan joint to divert the axial thrust loads away therefrom. The patent to Etnyre, U.S. Pat. No. 3,112,8O9, discloses the use of Cardan-type universal joints to couple the inboard and outboard ends of a live axle. Lateral forces on the wheel are disclosed as being resisted by the live axle and also by a cantilever leaf spring. The Cardan universal joints are disclosed as being capable of absorbing axial loads well in excess of those encountered under normal conditions, but such conditions are limited to use of the joints only as a drive member and not as a suspension member.
Being limited in their allowable articulation and not being able to carry axial thrust loads normally associated with an operating vehicle, Cardan-type universal joints are not used as a suspension member, thereby requiring other pivot points displaced outboard from such Cardan joint and additional suspension control members connected to such other pivot points to carry the axial thrust loads.
Constant velocity universal joints have heretofore been used with independent wheel suspension systems to avoid the debilitating effects of the foregoing cyclic speed variations of Cardan-type joints while permitting substantially greater articulation angles of the wheel with respect to the drive shaft or the drive shaft with respect to the differential of the power delivery unit. Constant velocity universal joints of the type that provide uniform velocity between the driving and driven members at any intersecting angle of the joint are shown in U.S. Pat. No. 2,046,584 to Rzeppa, U.S. Pat. No. 3,162,026 to Ritsema, and also commonly assigned U.S. Pat. Nos. 3,688,521, 3,928,985, 4,240,680 and 4,231,233, the specifications of which are hereby incorporated by reference. However, such known constant velocity universal joints have heretofore been used to carry just the driving torque transmitted through the spherical ball members of the joint. These balls ride in sets of opposing axial grooves formed on a partially-spherical inner joint member and on a partially-spherical outer joint member. Ball guide means, in the form of a cage, are positioned to capture and guide the balls through a homokinetic plane of rotation wherein the centers of the balls very nearly bisect the articulation angle between the spherical surfaces of the outer and inner joint members resulting in a constant velocity transmission of rotary motion. The ball cage normally consists of upper and lower partially-spherical surfaces guided, respectively, on the partially-spherical inner and outer surfaces of the joint members, but are designed to have radial clearances therebetween in order to ensure lubrication of the surfaces and thereby avoid excessive heat build up.
As explained more fully in the aforesaid U.S. Pat. No. 3,928,985, issued Dec. 30, 1975, when the connecting drive shafts transmit torque loads at an articulated angle, internally generated joint friction and joint geometry of such constant velocity universal joints cause the inner and outer joint members to shift with respect to each other to take up the aforementioned clearances. Balls in diametrically opposite sets of grooves are thrust in opposite directions, causing the cage to be somewhat tilted or skewed relative to the design. The forward and aft end portions of the upper and lower partially-spherical surfaces of the cage are tilted or skewed under torque transmitting loads and bear radially against the inner and outer spherical joint members. Such skewed contact between the inner and outer spherical surfaces of the cage with the respective inner and outer joint members is tolerated to avoid the undesirable friction effects of greater surface contacts with smaller clearances. The internally generated loads, as a result of torque transmission through the joint, have been observed to decrease from about a maximum of three hundred pounds per wheel, which occurs when maximum torque is transmitted at extreme articulation angles of the drive joints just before a vehicle begins to move.
In any event, the balls and axial grooves of the constant velocity universal joint have heretofore been used to translate the driving torque while the spherical portions of the inner and outer joint members experience the internally generated loads, such internally generated loads being carried either by direct contact between the inner and outer joint members or through the interposed spherical surfaces of the cage. As taught in U.S. Pat. No. 3,789,626, to Girguis, where one constant velocity universal joint was used as a fixed joint, as in the drive shaft of a rear drive motor vehicle, an object of such an application is to maintain the joint elements free of axial internal forces, even though the joint was constructed to absorb forces, at least those related to torque translation. In fact, the joint was designed to avoid transmitting axial forces through the control element. Therefore, when used at opposite ends of a driving half-shaft, one of such constant velocity universal joints has heretofore been of the axial slip or plunging variety, allowing axial movement of the driven joint with respect to the driving joint, and the constant velocity universal joint at the other end has been of the non-axial slip or fixed type not permitting such axial movement.
In any event, such constant velocity joints and the drive shaft that couple them have heretofore not been used to transmit anything more than torque loads, and the related internally generated axial loads. For example, U.S. Pat. No. 3,709,314, to Hickey, discloses the use of a Rzeppa or Bendix-Weiss type of constant velocity joint at both ends of each of two front-wheel drive shafts, and a Rzeppa type constant velocity joint is disclosed at both ends of each of two rear-wheel drive shafts. Hickey further discloses four suspension units of the type conventionally used to divert externally generated axial thrust loads away from the constant velocity universal joints. The suspension units are substantially similar, except for variations in torsion bar, shock absorber and linkage attachment points due to the location of the units, front to rear and side to side. Each typical suspension unit is disclosed as consisting of a conventional upper A-frame arm and lower A-frame arm. These are connected to tubular frame members by means of multiple brackets permitting vertical swinging motion. The wishbone ends of the A-frame arms are shown pivotably connected forward and aft of the center of each wheel, and in no instance is any drive shaft shown or disclosed as being any part of the suspension system or being a part of a typical suspension unit. U.S. Pat. No. 3,625,300 to Barenyi, et al., discloses the suspension of an axle unit of a motor vehicle by a support member permitting pivoting of the wheel pair in relation to the vehicle superstructure about two mutually perpendicular essentially horizontal axes, but without allowing any relative movement about either axis between the wheels and the axle gear housing.